This work describes a method to optimally transmit multimedia data over wireless fading channels via Orthogonal Frequency Division Multiplexing (OFDM). It is well known that multimedia data is sensitive to fading effects because each data bit varies in importance. Hence, reliable broadband wireless media communication systems maintain a number of very specific needs such as unequal error protection and time-varying bandwidth requirements, etc. Up to now, most OFDM systems allocate bits in a uniform manner across the subcarrier distribution. This type of methodology is fine for text data transmission with a performance measure in terms of the bit error rate (BER), but not sufficient to maintain high end-to-end visual quality for multimedia data transmission. To improve the overall system performance, we focus on optimal bit allocation in a rate-distortion sense. Our algorithm examines the data content and its associated performance and allocates the most important bits to the best channels in order to minimize the overall distortion. The proposed scheme demands channel state information that specifies estimates on the subcarrier quality distribution. It is demonstrated by experimental results that a significant gain in multimedia QoS is achieved with our approach with a layered video codec i.e. Motion JPEG2000.
A method to reliably transmit multimedia data over wireless fading channels by using a generalized OFDM technique is presented in this research. Multimedia delivery over wireless links is sensitive to fading effects. It is furthermore characterized by a number of different properties, including unequal error protection needs, time-varying bandwidth requirements, etc. Layered multimedia representation, such as MPEG-4 FGS, has been widely studied to meet these requirements. However, only this component is not sufficient to provide the desired quality of service (QoS). To further improve the overall system performance, we focus on the design of an adaptive modulation scheme, which maintains the ability to adapt to time-varying channel conditions as well as the layered multimedia representation. In particular, we study and analyze the performance of a technique known as Wavelet Packet Modulation (WPM) from the viewpoint of Orthogonal Frequency Division Multiplexing (OFDM), and demonstrate its application to wireless multimedia communication. In our framework, WPM is viewed as a general case of OFDM, which allows flexibility in terms of channel allocation and adaptability with respect to channel conditions. The algorithm demonstrates the flexibility of the new proposed method in transmitting multimedia data over interference-laden channels.
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